Read the Pew Research analysis

Back in 1982, Los Angeles’ African-American mayor Tom Bradley was leading Republican George Deukmejian in the polls in their race for the governership. Not only did he carry that lead right up to Election Day, but even exit polls on the day of the vote pointed to a Bradley victory. However, Bradley lost by a narrow vote and post-election studies suggested what has become known as the “Bradley Effect,” where fewer white voters cast their votes for him than the polls had predicted.

Hillary Clinton’s upset of Barack Obama in New Hampshire revived talk of the “Bradley Effect,” and now, Anthony Greenwald, a professor of psychology as well as of political science, has analyzed this season’s primary vote to see how much race is still a factor. His finding: pre-election polls did overestimate white support for Obama in states with small black populations, but the polls tended to underestimate Obama’s support in states with large black populations. All in all, by Greenwald’s math, the pollsters were off on the Obama-Clinton gap by more than 8 percentage points in 8 of 15 primaries.